1. Field of the Invention
The present invention relates to a relief valve for an oil pump, and more particularly, to a relief valve for an oil pump that can control oil pressure at the optimum level such that the main gallery is not damaged, and considerably decrease peak pressure in cold start.
2. Description of Related Art
In general, oil pumps are devices that suck oil stored in an oil pan and supply the oil to parts to lubricate.
The oil pumped up to an oil pump increases in pressure inside the oil pump and the oil that is discharged under high pressure from the oil pump may impact or damage an oil filter or a lubrication circuit.
Therefore, a relief valve that keeps the pumped oil at appropriated pressure is disposed at the oil outlet of the oil pump.
The relief valve keeps the oil-discharging pressure of the oil pump at an appropriate level and particularly prevents the main gallery from being damaged by high oil-discharging pressure by making bypass flow that returns some of the oil discharged from the oil pump to the oil pump or the oil pan, when the discharging pressure of the oil discharged from the oil pump to the main gallery of the engine increases above appropriate pressure.
FIG. 7 shows the configuration of a relief valve of the related art, in which a relief valve 200 of the related art includes: a plunger 201 that is disposed at a return hole 102 that is formed in a housing 100, perpendicular to the path of a discharging hole 101 through which oil is discharged to the main gallery of an engine, and bypasses some of discharged oil; a spring 202 that elastically supports plunger 201 in a spring chamber 203 having an air vent hole 204 exposed to the atmosphere at a predetermined distance from return hole 102; and a plug 203 that is thread-fastened to spring chamber 203 and support spring 202.
Therefore, plunger 201 directly carries the discharging pressure of the oil that is pumped by the oil pump and discharged outside through discharging hole 101, and when the discharging pressure of the oil largely increases, plunger 101 is pushed, thereby opening return hole 102.
As return hole 102 is opened by plunger 101, some of the oil discharged out through discharging hole 101 is bypassed to return hole 102, such that it can return to the oil pump or the oil pan.
The discharging pressure of the oil supplied to the main gallery of the engine, through discharging hole 101, can be kept at appropriate pressure by the return of the oil according to bypass due to return hole 102.
Control of discharging pressure of the oil can prevent the oil filter and the oil cooler from being damaged even in the cold start of the engine in which the oil pressure of the oil pump becomes relatively high, and particularly, it is possible to prevent the oil pressure at the main gallery of the engine from excessively increasing even if the number of revolution of the oil pump increases.
Relief valve 200 has the advantage of being able to quickly control the discharging pressure of the oil discharged outside through discharging hole 101.
However, it is required to ensure a sufficient relief margin to achieve quick response of relief valve 200, and accordingly, it is possible to maintain the oil pressure at the main gallery of the engine at an appropriate level, that is, to keep lubrication stable.
The capacity of the oil pump should be increased to keep the lubrication stable and the increase in capacity of the oil pump necessarily increase loss of fuel efficiency because the driving torque increases.
On the other hand, referring to FIG. 8 showing the property of oil that the viscosity increases at low temperature, it is difficult to keep appropriate oil pressure at the main gallery with relief valve 200 at relatively low oil temperature, such as in cold start or warm-up.
Further, relief valve 200 necessarily has a limit that it cannot appropriately control drop of oil pressure due to clogging of the oil filter for long-time use.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.